This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A. Structure of the plasminogen activator Pla from Yersinia pestis. Pla is a member of the omptin family, a family of outer membrane proteases that is widespread in gram-negative bacteria. While the physiological role of most omptins (such as E. coli OmpT) is unclear, Y. pestis Pla has a proven, very important role in the virulence of both bubonic and pneumonic plague by cleaving (activation of) human plasminogen. We are investigatng the high-resolution crystal structure of Pla inorder to gain information into the catalytic mechanism of omptins and the structural basis for substrate specificity. B. Structure of a full-length autotransporter. The autotransporter secretion mechanism is the most common mechanism for the secretion of virulence factors across the outer membrane (OM) from pathogenic Gram-negative bacteria. In addition, autotransporters have attracted biotechnological and biomedical interest for protein display on bacterial cell surfaces. Despite their importance, the mechanism by which passenger domains of autotransporters pass the OM is still unclear. The classical view is that the [unreadable]-barrel domain provides the conduit through which the unfolded passenger moves, with the energy provided by vectorial folding of the [unreadable]-strand-rich passenger on the extracellular side of the OM.